Investigation of Common-Mode Current Elimination in Four-Wire Inverter-Fed Motor

Abstract

Different concepts for mitigating common-mode (CM) current across the electric-drive system of an electric vehicle (EV) are evaluated in this paper. A traditional common-mode filter (CMMF) is designed and proved to be effective to reduce the leakage current in the three-wire topology. Even more reduction can be obtained in the four-wire topology, whether CMMF is installed or not. This is mainly due to the significantly decreased du/dt of neutral voltage in the four-wire topology, while the elimination caused by the CMMF is comparatively smaller. Besides, inserting CMMF to the four-wire topology can further reduce the CM current in some frequencies, at the price of some increase in other frequencies. Therefore, it is concluded that stronger elimination of CM current as well as avoiding bulky CMMF can be both realized through the utilization of four-wire topology. Even less CM current in the specific frequency range may be expected in this topology through optimized design of CMMF. These findings provide hints for mitigating CM current in an economic way and are validated by experiments on a practical electric-drive system.